1. Field of the Invention
This invention relates to a content addressable charge coupled (CCD) device memory and more particularly to such a memory where associative processing is performed concurrently on words but in sequential fashion with the words being properly aligned for comparison.
2. Background of the Invention
Addressing by content or associative addressing is a desirable feature for many computer memory applications. However, such content addressable memories are not widely used because of their costs. As a result, presently available content addressable memories are of relatively small size and also relatively expensive. With the advent of large scale integrated circuitry and, particularly, charge coupled devices (CCD's), memory manufacturing costs can be reduced and capacity increased to a large extent such that the application of content addressable or associative memories should become more practical and widespread. Prior art CCD memories were not normally designed to be content addressable. As a result, the content addressing or associative addressing are primarily done by softward techniques that, in turn, increase the memory accessing time. With the implementation of the content addressing functions into the memories themselves, faster and less expensive content addressable memories would become more readily available for information retrieval, filing, symbolic addressing and the like.
CCD memories are considered to be dynamic in the sense that the data bits are circulated in loops with the accessing of respective loops at particular locations. Basically, CCD's are fabricated as MOS or MIS integrated circuits, wherein potential wells are formed by the application of voltage pulses to the substrate to activate MOS or MIS capacitors. Voltage charges may be inputed and the charge pockets shifted along various points throughout the substrate by the proper application of voltage pulses to these capacitors. Refresh circuitry is required to maintain the magnitude of the charge pockets which would otherwise dissipate. Fabrication of the substrates and the means for moving the charge pockets around the substrates are well described in the prior art as illustrated by the Kosonocky U.S. Pat. Nos. 3,758,794 and 3,760,202. These patents also disclose signal regeneration circuits, methods and means for operating CCD's in plural phase configurations, and clocking and timing means. A number of papers which discuss the application and technology of charge coupled devices include W. S. Boyle and G. E. Smith, "Charge-Coupled Devices -- A New Approach to MIS Device Structures," IEEE Spectrum, July 1971; Altman, "The New Concept for Memory and Imaging: Charge Coupling," Electronics, June 21, 1971; J. E. Garnes and W. F. Kosonocky, "Charge-Coupled Devices and Applications," Corporate Engineering Services, RE-18-5-22, August 1972, page 78.
Since CCD memories sequentially circulate data, that data must be operated upon sequentially. It would be desirable to have a charge coupled device memory in which the data bits are circulated in a number of loops that are operated on concurrently to provide the appearance of word parallel processing and to ascertain that each of the words was properly aligned for content comparison and retrieval.
It is then an object of the present invention to provide a charge coupled device memory which is content addressable or associative addressable.
It is another object of the present invention to provide a content addressable charge coupled device memory wherein the content addressing function is performed by logic associated with the charge coupled device.
It is still another object of the present invention to provide a content addressable charge coupled device memory in which there is concurrent word processing.